Fabr's Car-VW/busa crossbreed

[trojan]

The pretzel arm is a real thing. Build em too light and they will morph into one.

[fabr]

I love pretzels,just not ON my car.hehehehe

[Engineer]

Looking good!

Is the rear parallel?

Is there a chance of seeing the front suspension cycle.......  I wanna see the cambre curve. 

Or are you still nailed down to the table?

[fabr]

It's still nailed down.Likely pull those nails tomorrow nite tho.Yes the rear arms are parallel. No camber gain.Looking for max travel .Any camber gain will reduce travel significantly. If this car was primarily for dirt/desert I'd likely have built in some camber gain and sacraficed a bit of travel.  But since this will see mostly sand I feel I'm good. The front is right off Rorty's plans for the R16.  A decision I may regret but.....................who knows. Got some spacers/bushings to make so I'll be able to give you some front camber pics soon. 

[Engineer]

It's still nailed down.Likely pull those nails tomorrow nite tho.Yes the rear arms are parallel. No camber gain.Looking for max travel .Any camber gain will reduce travel significantly. If this car was primarily for dirt/desert I'd likely have built in some camber gain and sacraficed a bit of travel.  But since this will see mostly sand I feel I'm good. The front is right off Rorty's plans for the R16.  A decision I may regret but.....................who knows. Got some spacers/bushings to make so I'll be able to give you some front camber pics soon.

That is eactly why I want to see it. 

[artie on edge]

. No camber gain.Looking for max travel .Any camber gain will reduce travel significantly. .

Can You explain to this dumbarse why this is so?

[fabr]

That is eactly why I want to see it. 

No rake. I'll let you know the curves as soon as I can.

[Engineer]

Can You explain to this dumbarse why this is so?

If the wheel goes into positive camber as it is dropping to full extension (droop), that means that the top of the tire is leaning in.  When you look at the axle from the rear, at full droop, the axle is coming down from the inner CV to the outer CV, and it turns an angle into the stub shaft.  This is where maximum droop is determined, because maximum angle on the CV is reached here. 

Now if you add 3 degrees of camber, then that camber adds to the angle between the stub shaft and the axle.

So if the last 3 degrees, from 22deg to 25deg represents 1.5" of wheel travel, then you won't get that last 1.5 inch because 25 degrees that the outer CV see's actually occurs then the axle is at 22 degrees.

Let me start again.  If you have 3 degrees of camber, then the stub shaft (wheel) and the transmission shafts are not parallel, so the outer CV is seeing an additional 3 deg that the inner is not.  So the outer will be at 25 deg when the inner is at 22.

 

If I haven't explained it just say so and I will draw a picture. 

[fabr]

Can You explain to this dumbarse why this is so?

think about it this way:droop is limited by the misalignment angle of the cv.A 930 is OK at 25*. If 2-3 degrees is taken up with camber gain in droop you lose 2-3 degrees droop travel.

[fabr]

UHhhh,engineer said it better.

[Nutz4sand]

If the wheel goes into positive camber as it is dropping to full extension (droop), that means that the top of the tire is leaning in.

Please correct me if I am wrong here. But with the tire leaning out from the frame (at the top of the tire) its positive so if it leaned out or positive at the bottom that would allow more travel in droop.

Thats why you want it to go negative at the top of its travel as well ( beside tire roll) as if its negative at the top it leans in and is less angle on the CV.

But a suspension that creates negative camber at the top usually does it at the bottom (droop) and thats where it takes the angle up with the tire leaning IN (negative) as the tire apporaches its lowest point. 

[fabr]

Actually there's not much worry in bump as the cv doesn't see nearly as much angle as droop.

[Engineer]

Please correct me if I am wrong here. But with the tire leaning out from the frame (at the top of the tire) its positive so if it leaned out or positive at the bottom that would allow more travel in droop.

Thats why you want it to go negative at the top of its travel as well ( beside tire roll) as if its negative at the top it leans in and is less angle on the CV.

But a suspension that creates negative camber at the top usually does it at the bottom (droop) and thats where it takes the angle up with the tire leaning IN (negative) as the tire apporaches its lowest point.

It really wouldn't allow more travel than zero camber, because then you are limited by the inner CV.


I think it is usually built in for the concept of keep the tire straight in the presence of body roll.  Also, most designs would be hard pressed to reach max angle in compression unless you have really tall tires, or like plowing with the frame. 


I would like to see this in a real life car.  I have been drawing like crazy, and it takes a really short upper arm to get this to happen.

[Nutz4sand]

OK but just pointing out you said positive camber is leaning in and leaning in is negative. Outward is poisitve.

[artie on edge]

If the wheel goes into positive camber as it is dropping to full extension (droop), that means that the top of the tire is leaning in.  When you look at the axle from the rear, at full droop, the axle is coming down from the inner CV to the outer CV, and it turns an angle into the stub shaft.  This is where maximum droop is determined, because maximum angle on the CV is reached here. 

Now if you add 3 degrees of camber, then that camber adds to the angle between the stub shaft and the axle.

So if the last 3 degrees, from 22deg to 25deg represents 1.5" of wheel travel, then you won't get that last 1.5 inch because 25 degrees that the outer CV see's actually occurs then the axle is at 22 degrees.

Let me start again.  If you have 3 degrees of camber, then the stub shaft (wheel) and the transmission shafts are not parallel, so the outer CV is seeing an additional 3 deg that the inner is not.  So the outer will be at 25 deg when the inner is at 22.

 

If I haven't explained it just say so and I will draw a picture. 

Pic not required, I gotcha! I wasnt thinking about the CV issue I was just wondering how camber effected travel and couldnt see it. Now its as clear as , thanks guys.

Another question on the same line. Ive watched many many larger offroad buggys which seem to have nil or very little camber change on compression. Thi sis ok when going through whoops etc but when cornering you very often see the outside tyre leaning out.

Ive been asking myself "why?" recently and then I saw Fabr's posting and went 'hello'.

These cars 'seem' to have a a long and short arm set up and then dont seem to change much (as in the difference in lengths isnt enough). IS there a reason why so many of them dont do it? Again, I am the resident dumbarse...